Interpretive Summary: Glyphosate is a broad spectrum herbicide used for efficacious control of weeds in glyphosate-resistant crops. In glyphosate-resistant wheat, it was found that plants had significantly less rust, when sprayed with glyphosate. This study shows that glyphosate may accumulate to levels in the leaves that may inhibit the growth of important rusts, such as stripe and leaf rust of wheat, and Asian soybean rust.

Technical Abstract:
Glyphosate is a broad spectrum herbicide used for efficacious control of weeds in glyphosate-resistant crops. Glyphosate inhibits 5-enolpyruvyl shikimate 3-phosphate synthase, a key enzyme in the synthesis of aromatic amino acids in plants, fungi and bacteria. Studies with glyphosate-resistant wheat showed that glyphosate provided both preventive and curative activities against Puccinia striiformis f. sp. tritici and Puccinia triticina, which cause stripe and leaf and rusts in wheat, respectively. Wheat rust control was demonstrated at multiple plant growth stages with a glyphosate spray rate typically recommended for weed control. Rust control was absent in formulation controls without glyphosate, dependent on systemic glyphosate concentrations in leaf tissues, and not mediated through induction of four common systemic acquired resistance genes. A field test with endemic stripe rust inoculum confirmed the activities of glyphosate pre- and post-infestation. Preliminary greenhouse studies also demonstrated that application of glyphosate in glyphosate-resistant soybeans suppressed Asian soybean rust, caused by Phakopsora pachyrhizi.